This invention relates to a method and apparatus for detecting the presence of an adhesive on a travelling web. In particular, the invention relates to a method and apparatus that employs specular reflectance to determine the presence of a coating on cigarette tipping paper.
The improper application of adhesive to cigarette tipping paper has been shown to cause severe performance defects in a cigarette. In the cigarette rod can come apart from the filter while the smoker is pulling the cigarette from the pack, in the visual appearance of the product, and insufficient adhesive can impair the performance of the cigarette by changing the draft/dilution characteristics of the cigarette. In the extreme case, insufficient adhesive can cause a burning rod of tobacco to unexpectedly detach from the filter.
All of the aforementioned occurrences are a result of insufficient adhesive being applied to the edge of the tipping paper. For satisfactory adhesion, there must be at least 2 mm of adhesive on the outermost 5 mm of the tipping paper. It would be desirable, therefore, to have a method or device for detecting the presence of the adhesive as well as for quantitatively measuring the width of the adhesive applied to the tipping paper. Such a method or device would have to be capable of inspecting the tipping paper in the cigarette maker at speeds of up to 2.0 meters/second.
Systems have been developed for detecting the presence of he adhesive on a travelling web. U.S. Pat. No. 2,141,052 discloses a system that measures the resistance of the paper as an adhesive is applied. The system disclosed, however, requires undesirable direct contact with the moving web. U.S. Pat. No. 4,417,934 discloses a non-contact system that employs capacitive sensing to detect the presence of the adhesive. While this system avoids direct contact with the web, it is not suited to quantitatively measuring the width of the applied adhesive.